Envelope for, and method of processing, a color cathode-ray tube

ABSTRACT

In one step of the screening process, the shadow mask of a color tube is mounted from studs provided in the faceplate section. The faceplate is then introduced into an exposure chamber where it is supported at three points spaced along the sealing land near the locations of the support studs. This establishes the faceplate in a reference mode, free of twisting moments and elastic deformation. When the screening process is completed, the faceplate is superposed over the enlarged end of the funnel section of the tube envelope and supported therefrom at three spaced points similarly disposed along the sealing land of the funnel to engage the faceplate at the same spaced points of support effective in the exposure step. This re-establishes the faceplate in its reference mode. Frit sealing material is disposed between the sealing lands of the envelope sections and the assembly is heated to seal the faceplate and funnel to one another along the entirety of the sealing lands.

United States Patent [191 Palac RAY TUBE [75] Inventor: Kazimir Palac, Carpentersville, Ill.

[73] Assignee: Zenith Radio Corporation, Chicago,

Ill.

[22] Filed: Apr. 28, 1971 [21] App]. NO.: 138,073

[52] [1.8. CI. ..220/2.l A, 65/58 [51] Int. Cl ..H0lj 61/30, HOlk 3/22 [58] Field of Search ..65/42, 43, 58;

[56] References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS 692,228 6/1953 Great Britain ..220/2.3 A

[ 1 June 5, 1973 Primary Examiner-M. Henson Wood, Jr.

Assistant Examiner-John J. Love Att0rneyJohn J. Pederson and Cornelius J. OConnor [57] ABSTRACT In one step of the screening process, the shadow mask of a color tube is mounted from studs provided in the faceplate section. The faceplate is then introduced into an exposure chamber where it is supported at three points spaced along the sealing land near the 10- cations of the support studs. This establishes the faceplate in a reference mode, free of twisting moments and elastic deformation. When the screening process is completed, the faceplate is superposed over the enlarged end of the funnel section of the tube envelope and supported therefrom at three spaced points similarly disposed along the sealing land of the funnel to engage the faceplate at the same spaced points of support effective in the exposure step. This reestablishes the faceplate in its reference mode. Frit sealing material is disposed between the sealing lands of the envelope sections and the assembly is heated to seal the faceplate and funnel to one another along the entirety of the sealing lands.

6 Claims, 6 Drawing Figures PATENTEDJUH 5 I975 SHEET 2 BF 2 ln\ entor Kazamlr Polclc Afior y ENVELOPE FOR, AND METHOD OF PROCESSING, A COLOR CATHODE-RAY TUBE BACKGROUND OF THE INVENTION Color cathode-ray or picture tubes come in a variety of sizes and shapes and are formed of a multisection envelope of which the faceplate and funnel are major components. The faceplate has a screen area and a circumscribing flange the free end of which serves as a sealing land. The edge at the large end of the funnel likewise constitutes a sealing land which matches the faceplate with respect to size and configuration. While tubes may be round or rectangular, the rectangular shape is currently the more popular.

The envelope is sectioned, as described, to facilitate the application of various phosphor materials to constitute an image screen. Here again, there is a choice as to structure but usually the screen is an interlaced pattern of green, blue and red phosphors. They may be arrayed in a repeating sequence of stripes or, more usually, they may be phosphor dots collectively defining a multiplicity of color triads regularly disposed throughout the screen area.

The screen is photographically printed in a process that is very well known. Basically, a photoresist material which becomes insoluble in water upon exposure to actinic energy, such as ultraviolet light, is prepared as a slurry having one phosphor material suspended therein. The faceplate is given a coating of the slurry and the color-selection electrode or shadow mask is then installed in position within it. Thereafter, this subassembly is put into a lighthouse or exposure chamber where the slurry layer is exposed to light through the shadow mask. This creates a latent image of the pattern of that phosphor which is subsequently developed by removing the shadow mask and washing the panel with water. Repeating this general process three times, utilizing different phosphor slurries on each occasion and appropriately positioning the exposure light source, accomplishes photographic printing of all three phosphor materials on the screen after which the faceplate and funnel sections are united to one another.

Integrating these envelope sections is a well known technique employing a frit type of glass-sealing material. The frit is usually applied to the sealing land of the funnel with the funnel supported in a generally vertical position and the faceplate is then superposed thereover with the two sealing lands in registration with one another. The envelope assembly is then heat treated in an oven having an appropriate heat profile and time cycle to permit the frit to establish a vacuum type seal all along the sealing lands of the faceplate and funnel.

This entire process is well understood and is successfully practiced in the production of shadow mask color tubes on a mass production basis. Great care is exercised in the fabrication of the component parts and in the various processing steps to assure proper and precise beam landings in the finished tube. For example, the sealing lands of the faceplate and funnel are frequently precision ground in an effort to attain an optimum mating of these sections in the sealing process. And yet, beam landing errors are encountered.

If the tube in process is of the shadow mask variety with phosphor dot triads to be excited by a cluster of three electron guns, the three beams ideally are concentric with the phosphor dots on which they impinge. Deviation from this condition of registration is the condition referred to as a beam landing error. It has been suspected heretofore that the sealing edge of the face-- plate panel experiences viscoelastic deformation in the sealing cycle resulting in a shift or displacement of the mask relative to the panel and consequently producing beam landing errors. This conclusion was reached because it was observed that there was very little, if any, shift of the mask relative to the screen as the faceplate panel was introduced into the various exposure chambers required in processing the three phosphors but a shift did result when the panel was placed on the funnel and sealed. I

Applicant has discovered that viscoelastic deforma-f tion is not the cause of the mask to panel shift and'hasfurther determined that the panel exhibits the property of elasticity to a sufficient extent that, even at ambient temperatures, the sealing land of the panel accommodates or conforms to the specifics of the sealing land of the funnel and for this reason is a principal source of beam landing error. The present invention obviates or minimizes this aspect of beam-spot misregistration.

Accordingly, it is an object of the invention to provide a novel envelope, and a new fabricating technique, for color picture tubes which reduces beam landing errors.

It is another object of the invention to provide a novel color tube envelope in the processing of which superior results are attained in respect of beam landing errors.

Another specific object of the invention is to improve the processing of color picture tubes to reduce beam landing errors.

SUMMARY OF THE INVENTION An envelope for a color cathode ray tube in accordance with the invention comprises a faceplate section having an image area and a circumscribing flange the free end surface of which constitutes a first sealing land of a given size and configuration. The funnel section of the envelope likewise has a free end surface, usually its large end, which constitutes a second sealing land corresponding in size and configuration to that of the faceplate. At least one of these envelope sections has a plurality of spaced supports projecting from and disposed along the sealing land thereof for achieving support of the faceplate at spaced points as distinguished from the linear or planar support of prior envelope structures.

The processing aspect of the invention includes the steps of photographically printing the screen with different phosphor materials, essentially as described above, in which process the faceplate, with the colorselection electrode or mask supported within it, is exposed while being supported at three spaced points along its sealing land, establishing the faceplate in a reference mode in which the panel is free of deformation and twisting moments. After the printing step, and with the funnel substantially vertically disposed with its sealing land uppermost, the faceplate is placed on the funnel with the two sealing lands facing and in registration with one another, with a frit-sealing material disposed between the sealing lands, and with the faceplate supported from the funnel through a plurality of spaced contacts disposed along the sealing lands to reestablish the faceplate in its aforesaid reference mode. This assembly is then subjected to a heat treatment to seal the faceplate and funnel to one another along the entirety of the sealing lands.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a portion of an exposure chamber and the faceplate section of a picture tube in process;

FIG. 2 is a plan view, partially broken away, of the faceplate in the exposure position;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2; v

FIGS. 4 and 5 represent steps in the sealing of the faceplate and funnel sections;

while FIG. 6 shows a novel form of funnel section.

DESCRIPTION OF THE PREFERRED EMBODIMENT For convenience in describing a specific embodiment of the invention, it will be assumed that the color cathode-ray tube in process is rectangular in shape, has a mosaic type screen comprised of a multiplicity of phosphor dot triads, and has acolor-selection electrode in the form of a rectangularly shaped shadow mask with a field of apertures through which three electronbearns have access to the screen to excite the phosphors thereof. The faceplate 10 has a screen or image area 10a and a circumscribing flange 10b and provisions, such as inwardly projecting mounting studs 10c, for removably supporting the shadow mask to facilitate its insertion and removal as required in various stages of manufacture, especially during screening. The free end 10d of the faceplate constitutes a sealing land of a given size and configuration; for the case underconsideration it is rectangular in shape and may be 23 inches in diagonal dimension.

The color-selection electrode or shadow mask 1 1 has a multiplicity of apertures 11a uniformly distributed over a rectangular field and a frame 11b to which the apertured component is attached. Mounting springs 110 are secured at one end to the frame and have an aperture at the free end for engaging mounting studs 10c to position the mask within faceplate 10 with a desired spacing relative to screen 10a. Both three and four point suspension systems are known but, for the case illustrated, only three mounting springs are employed.

One is located in the central part ofthe uppermost periphery of the mask and the other two are located sym metrically on the two sides of the mask with the apertured ends disposed below the central axis. This is a conventional structure which is easily inserted into and removed from faceplate 10.

As described above, phosphor dots are photographically printed on screen area 10a through a process that is very well known and need not be described here in any detail. One necessary.step is the exposure of the inner surface of screen 10a with actinic energy after that surface has received a coating of a phosphor hearing photosensitive resist. That step, which is of interest to the present discussion, takes place in an exposure chamber or lighthouse 12 which is indicated in FIGS. 1 and 3. It is a conventional structure including a source (not shown) of ultraviolet light, such as a mercury arc lamp, positioned to simulate the electron beam of the tube which is assigned to excite the particular phosphor ingredient of the slurry coating. The coated faceplate, with its shadow mask 11 in position, is supported at a plurality of spaced points disposed along its sealing land 10d rather than having a line contact along the entirety of the sealing surface. This is achieved by means of three pads 12a secured to a shelf 12b which has an aperture or cutaway area 120 of essentially the same size and configuration as screen 10a.

erly installed in its exposure position, is supported at three points through the engagement of these pads with sealing surface 10d at essentially the location of mounting studs 100 as illustrated in FIG. 2. The supports establish the faceplate in a reference mode, that is to say, in a rest condition in which the faceplate experiences neither deformation nor twisting moments because the pads are positioned as described to exert equalized supporting forces at the three points of support. It is common practice to have vertically extending positioning posts 12d on table 12b topermit rapid and precise positioning of faceplate 10 on the exposure chamber.

The validity of this three point support of the faceplate in the exposure position has been established in that examinationshows that the reference condition exists when. the faceplate is installed in any of the three exposure chambers generally used in screening where the prevailing practice is to assign one such chamber to the processing of one of the three color phosphors. In other words it is found that the space relation of shadow mask 11 relative to screen 10a is essentially the same in all three exposure chambers which is the condition to be maintained if beam landing errors are to be avoided or at least minimized.

After all three color phosphors have been applied to the screen by the photographic resist process featuring exposure of the faceplate for each such phosphor, the screen is filmed and aluminized in a well known manner and is then ready to be sealed to the funnel section and assigned to the assignee of the present invention. 7

The large and free edge 13a of the funnel constitutes a second'sealing land which has the same size and configuration as land 10d of the faceplate in order that they may properly register with one another The first step i of the sealing operation isplacing faceplate 10 on funnel l l with sealing lands 10d and 13a facing and inregistration with one another, with a frit material 15 deposited between the lands, and with faceplate l0 ,sup-

ported from funnel l3 through a plurality of spaced 7 contacts disposed along the sealing lands to re-establish faceplate 10 in its aforesaid reference mode. The necessary condition to be attained is re-establishing the faceplate in its reference mode and this condition may be satisfied in a variety of different ways. For example, high spots may be provided in the sealing land of either faceplatelO or funnel l3; alternatively, particularly when processing a tube having an envelope of conventional construction, shims or other support elements may be positioned at the proper locations on .sealing land 13a before the faceplate is placed on that land. FIG. 4 illustrates this approach in which'shims 16 of very small area are placed on sealing land 13a to engage land 10d of thev faceplate preferably at the same spaced points at which the faceplate was supported during exposure. An important consideration is that the envelope sections 10 and 13 are supported at spaced points chosen to establish the faceplate in its reference mode as distinguished from past practices wherein the sealing lands are in line or continuous contact with one another. The shims 16-may be ballpoints, small glass 7 rod segments or any material which affords the necessary mechanical support of the faceplate and is compatible with the envelope sections and the sealing material applied to these component parts to effect a vacuum type seal between them. Usually, a frit-seal composition is applied to scaling land 13 and also to all surfaces of shim 16 after which faceplate is placed upon the shims. The envelope is now ready for sealing and this is accomplished by subjecting the assembly to heat treatment in a lehr having the appropriate temperature profile and time cycle to seal the faceplate and funnel to one another along the entirety of the sealing lands. Of course, the material of which shims 16 are formed must retain its mechanical and physical integrity during the heat treatment or sealing process. For a 23 inch rectangular tube the shims may be formed of glass or ceramic having the same thermal expansion coefficient as the funnel glass. The shims should be electrical insulators and present a support area of approximately 0.0625 square inch and a height of approximately 0.015 inch. Satisfactory results have been obtained through the use of glass rod segments having a diameter of 0.015 inch and a length of 0.5 inch. Flat shims, having a support area of 0.25 X 0.25 inch and a thickness of 0.015 inch, are also suitable.

FIG. 6 represents a novel form of funnel 13 which has raised elemental areas 16a on its sealing land at places corresponding to the locations .of shims 16 in FIG. 4. This is an approach in which the spaced supports are formed integrally with the funnel and this may be achieved by molding or by grinding in fabricating the funnel.

Measurements have been made of color picture tubes fabricated in accordance with the present invention which verify the efficacy of thedescribed process in reducing beam landing errors attributable to deformation of the faceplate in sealing. By supporting the faceplate at spaced points relative to the funnel, rather than having them in line contact, one is able to establish the faceplate in its reference mode and the desired spaced relation of mask 11 relative to screen 10a is preserved to a much higher degree of accuracy than with prior practices in which sealing lands of the faceplate and funnel engage in line contact. Because of the property of elasticity exhibited by the face panel, the line contact of these envelope sections permits the panel flange to accommodate to the funnel and in a great many instances result in an undesirable change in the mask to screen space relation, leading to beam landing errors. Practicing the present invention not only reduces the change in mask to screen spacing but is further attractive in that it makes unnecessary the expense of prior procedures in grinding the landing surfaces of the envelope sections.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims-is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

l claim:

l. A multi-section envelope construction for a color cathode-ray tube for preventing beam landing error attributable to the conformation of one section of said envelope to another, said envelope construction comprising: I

a faceplate section having an image area, which is formed while said faceplate section is established in a reference mode and in which said faceplate is free of deformation and twisting moments, and a circumscribing flange the free end surface of which constitutes a first sealing land of a given size and configuration;

and a funnel section having a free end surface which constitutes a second sealing land of said size and configuration;

one of said sections having a plurality of spaced supports projecting from and disposed along the sealing land thereof for reestablishing said faceplate section in said reference mode and for constituting the supporting means for establishing a predetermined spacing between said faceplate section and said funnel section. 2. A'color cathode-ray tube envelope in accordance with claim 1 in which said spaced supports project from said sealing land of said funnel section.

3. A color cathode-ray tube envelope in accordance with claim 2 in which said spaced supports are formed integrally with said sealing land of said funnelf 4. A color cathode-ray tube envelope in accordance with claim 3 in which three supports project from said sealing land of said funnel section.

5. A color cathode-ray tube envelope in accordance with claim 4 in which said faceplate has three mounting studs projecting inwardly from said flange to support a color-selection electrode within said faceplate,

and in which said supports of said funnel are positioned on the sealing land thereof to be in substantial alignment with said mounting studs of said faceplate when said faceplate is supported from said funnel. 6. A multi-section envelope construction for a color cathode-ray tube for preventing beam landing error attributable to the conformation of one section of said envelope to another, said envelope construction comprising:

a faceplate section having an image area, which is formed while said faceplate section is established in a reference mode and in which said faceplate is free of deformation and twisting moments, and a free end surface which constitutes a first sealing land of a given size and configuration; and a funnel section having a free end surface which constitutes a second sealing land of said size and configuration; 7

one of said sections having a plurality of spaced supports projecting from and disposed along the sealing land thereof for reestablishing said faceplate section in said reference mode and for constituting the supporting means for establishing a predetermined spacing between said faceplate section and said funnel section. 

1. A multi-section envelope construction for a color cathode-ray tube for preventing beam landing error attributable to the conformation of one section of said envelope to another, said envelope construction comprising: a faceplate section having an image area, which is formed while said faceplate section is established in a reference mode and in which said faceplate is free of deformation and twisting moments, and a circumscribing flange the free end surface of which constitutes a first sealing land of a given size and configuration; and a funnel section having a free end surface which constitutes a second sealing land of said size and configuration; one of said sections having a plurality of spaced supports projecting from and disposed along the sealing land thereof for reestablishing said faceplate section in said reference mode and for constituting the supporting means for establishing a predetermined spacing between said faceplate section and said funnel section.
 2. A color cathode-ray tube envelope in accordance with claim 1 in which said spaced supports project from said sealing land of said funnel section.
 3. A color cathode-rAy tube envelope in accordance with claim 2 in which said spaced supports are formed integrally with said sealing land of said funnel.
 4. A color cathode-ray tube envelope in accordance with claim 3 in which three supports project from said sealing land of said funnel section.
 5. A color cathode-ray tube envelope in accordance with claim 4 in which said faceplate has three mounting studs projecting inwardly from said flange to support a color-selection electrode within said faceplate, and in which said supports of said funnel are positioned on the sealing land thereof to be in substantial alignment with said mounting studs of said faceplate when said faceplate is supported from said funnel.
 6. A multi-section envelope construction for a color cathode-ray tube for preventing beam landing error attributable to the conformation of one section of said envelope to another, said envelope construction comprising: a faceplate section having an image area, which is formed while said faceplate section is established in a reference mode and in which said faceplate is free of deformation and twisting moments, and a free end surface which constitutes a first sealing land of a given size and configuration; and a funnel section having a free end surface which constitutes a second sealing land of said size and configuration; one of said sections having a plurality of spaced supports projecting from and disposed along the sealing land thereof for reestablishing said faceplate section in said reference mode and for constituting the supporting means for establishing a predetermined spacing between said faceplate section and said funnel section. 